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MG Midget and Sprite Technical - custom anti roll protection attach points
I am now ready to install serious anti roll protection.
Since this is also an oportunity to stiffen up the body I want to think about it carefully so that I can maximize the chance to do it right.
The roll over part will be a typical hoop that is welded to a reinforcement plate at the lowermost part of the rear "shelf" near the door on each side. then there will be the cross bar for seat belt attachment. then there will be a diagonal brace. from one top corner to the oposite lower corner.
then I plan on putting two rearward braces that will go into the trunk and anchor somewhere that maximizes safety and is a good place to double as body stiffener.
then I plan on putting one diagonal brace from about 1/3 out from the drivers side of the top of the main hoop to somewhere near the passenger left foot (passing somewhere to the right of the gear shift knob).
It is also possible that I will add a tube that goes across just under the panel which joins up with something that goes along the sides (but there might not be room for that.
Does anyone have any pictures of the attachment points for something like this?
I have not weighted my car yet. If it is going to be over 1500 lbs then the wall thickness of the tubes has to go one higher. John McCues car weights under 1500 lbs. I have no idea what mine weights or whether I should even bother trying to get it below 1500.
I have not even calculated what this tubing will weight yet (not the slightest idea how much weight I am adding). After I make some estimates with a tape measure I will decide how much of a problem the weight will be.
I hope that someone has some nice photos of something similar. Particularly something that shows the best way to stiffen the body at the same time.
|Rebecca, it sounds like your bar will be very similar to the one I built for my car. I made mine a bolt in bar, but for a weld in bar the attachments are basically the same minus the lower reinforcement plates. The main hoop attaches with a plate of 1/4" thick steel that was formed to match the body panel. It should be a minimum of about 4" X 4" to distribute the loads to the sheet metal of the chassis. On the rear braces and the front Petty bar brace I used some right angle material that attaches through the frame rail from the side with the bar welded to the top surface. For a bolt on bar use some tubing where the bolts pass through the frame rails to keep from crushing the structure as you tighten. The rear brace bolts wind up coming through the rear wheel well area and the Petty bar brace bolts come through beside the transmission. Sorry no photos of the actual attachment points and I've lost the construction photo of the roll bar out of the car for paint.|
As for the weight, the extra weight of the increased tubing size is going to be minimal and you'll have to strip the car completely to get it down to under 1500 pounds so go for the larger tubing the rules call for on the main hoop. If I remember correctly that's the only part that has to be the larger size, the braces can still be the smaller diameter. That's what I did, a larger main hoop with the smaller diameter braces. I've never had it checked by the SCCA, but had no problems with the local autocross club safety inspection.
|larger main hoop. I had not thought of that. good idea. and I will be drilling an access hole for inspection so that they can verify it. I will do my homework and make all of the required pieces thicker (might be more than just the main hoop but I will check). I am thinking that all of the required pieces (including all of the braces except for the extra forward ones that I want to add).|
Here are some pics of Bill's midget that may help:
Sorry the first shot is hazy. I'd just gone from an air-conditioned condo to the heat and humidity outside, and my camera fogged up. Gotta love Midwestern summers!
Hope this helps,
|wow great pics. I looked at them all (I did not find any good shots of the actual points where rollover protection is welded in though).|
What event was that? Where was it? I would love to attend such an event if it happens in the north east.
I will try to take some pics of the cage in my race car which is not dissimilar to what you suggest
|Unless you are spaceframing the rear I would refrain from putting braces rearwards of the rear main hoop attachments.|
My reasoning is that should you hit/get hit in a rear 1/4 shunt or rear end shunt then the bars will be pushed forwards, destroy your lovely cage and in turn write off the shell as that pressure will then be transferred to all attachment points.
This is the reason UK insurance companies dont like roll cages in road cars. What may be a light shunt can effectively write a car off through transfer through the cage.
In the event of a roll, I would be more concerned with protecting the area you are in, sod the car. As such the likes of the safety devices 6-point is ideal. You also dont want to create veritable javelins should an impact cause any of the welds to fail. All of this is taken into consideration for our MSA approval along with tube diameter, quality, type of welds and reinforcement of attachment points.
|Peter, over here SCCA rules require a rear brace from each leg of the main hoop and at an angle of 30 degrees. That places them towards the rear edge of the wheel well area in a Spridget. |
From the SCCA rule book.
(Cars must have 2 braces extending to the rear from the
main hoop and attaching to the frame or chassis. Braces
must be attached as near as possible to the top of the
main hoop (not more than 6 inches below the top), and at
an included angle of at least 30 degrees)
Tubing size is according to vehicle weight. I was wrong earlier, it all has to meet the minimum size. In my bar the main hoop is larger material than the minimum for it's weight and the braces are the required size.
GCR Vehicle Weight Tubing Size (inches)
(outer diameter x wall thickness)
Up to 1700 lbs 1.375 x .080
1701 - 2699 lbs 1.500 x .095
1.625 x .080
2700 lbs and up 1.750 x .095
1.625 x .120
Maybe i didnt word that correctly
Main hoop yes, main hoop Rear legs yes, attached to chassis legs yes, but all the way into the boot - nope.
this looks scary.
|That is Prop looking at Bill's car.|
|Rebecca, Gryf took the photos at our Sprite 50th. He's a great photographer as you all probalby know. I took some detail shots of my roll bar attachments last night but didn't get them downloaded from my camera. I'll do that tonight and post them for you. With a taller bar the rear legs will fall a little further to the rear when installed at the required 30 degree angle. Mine are a bit less than that so that I could still have room for the folding hood. For a proper race legal bar for SCCA autocross that's one thing that you will most likely have to forfit, the use of the folding hood. Either the bar will be too high to clear it with a 2" clearance above your helmet or the rear braces will fill the area where it needs to fold. My car is modified so would run E Mod and need a bit more complex bar than a street tire stock class, if you keep your car pretty stock and off slicks you will require a bit less complex roll bar. By the current rules I would have to remove my windshield to get by in my class with a single hoop bar, I should have a front hoop as well.|
Absolutely disagree having gone in backwards in a FISC race at Barcroft at Croft in '00 at over 100mph - If I hadn't had roll cage legs behind the rear axle line the shell would have been scrap - as it is we put new boot floor in it and it went on to win the Midget Challenge class B championship in '02.
Sometime later in a FISC race at Dijon the shell finally met its match when a competitor spun and parked it in front of me - unfortunately I hit him sideways which bent the entire shell like a Banana... I walked away - he was taken away in an ambulance unconscious... There were a number of drivers who saw the protection my cage gave me and looked a bit sick when they thought what would have happened if they had had the same accident in their car.
IMHO the standard SD cage does not provide sufficient strength or protection in a race Midget unless you weld the door bars in - and even then I choose to have a deal more protection around me than that...
I will try to post some pictures of my present car over the weekend
|Rebecca, here's a link to my Flickr gallery of the event that Bill mentioned. (And thanks for the kudo!!)|
|Rebecca, here are the detail shots of how I attached my roll bar.
Rear leg second bolt in boot area.
Rear leg front bolt in cockpit.
Petty bar in passenger side center rail. Grade 8 hardware used at all points.
|Thanks for the pictures!|
Was that one of the maroon cars built by Mike Johnston for Pat Cochrane. Young fella driving it when it got the side impact?
If so then you have a chassis designed and built by an absolute genius with a huge wealth of experience. Not someone throwing a few tubes together with a welder. As such I would suspect that it probably still lives on today in one form or another.
You have to remember that she isn't racing iirc. Just autosolo stuff. I may be wrong.
There is no point in filling your car with weight and pointless lengths of tubing. Make sure it is stiff and the passenger compartment is a safe place to be. If I end up in an huge accident I don't think I'd be overly worried about how the car looked or survived providing I did.
|I would like to have door bars but I don't know yet if they will fit with the seats (I will find out soon). I may be able to test set one possible seat this weekend.|
I think that I am going with either Sparco sprint 5 or Corbeau classic bucket (or both - swappable). I think that it would fit with the Corbeau but we shall see.
This is the rear fixing for the safety devices cage in my step fathers race car...
|This is a shot inside my car showing the door bar
|Behind the seat the black bar is bolted across the chassis rails and is what the seat belts are mounted to
|The rear hoop supports pass through the rear bulkhead and mount to the rear leaf spring mounts on the chassis rail
|The front hoop is attached to a box section on the bulkhead
|Rear hoop mounting|
Hope this helps
|These pictures are really helpful. thanks.|
This thread was discussed between 19/10/2010 and 25/10/2010
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.